Automated railroad traffic control systems which include the operations of a general purpose digital computer have been disclosed in U.S. Pat. Nos. 3,838,768 and 3,976,272 both of which patents are assigned to the assignee of this application.
In the first-mentioned patent, a traffic control system is disclosed in which a digital computer is employed to monitor railroad operation, although all initial decision-making operations are left to a human operator. In that system, the general purpose digital computer receives inputs from the railroad area which is being controlled and maintains a description of the condition of the area at all times. The computer also controls a visual display so that the human operator is informed of railroad conditions. Based upon the display, the operator may initiate control requests to alter the condition of the railroad so as to facilitate train movements which he deems necessary or desirable. For example, the operator may clear a signal, request the repositioning of a track switch, etc. The digital computer then monitors the operator's judgments by determining whether or not the operator's control requests are valid in light of existing traffic conditions. For example, the system will prevent the operator from clearing a signal into an occupied track section or throwing a switch which is occupied, etc.
The system disclosed in U.S. Pat. No. 3,976,272 is more sophisticated in that it eliminates the necessity for detailed operator intervention, and can, under certain conditions, make decisions for itself and implement those decisions, automatically. For example, the operator may direct the system to clear a route for a particular train from an entrance to an exit location in the railroad. The system is capable of implementing this request and selecting a preferred route where more than one is available, although the operator does not designate the particular route the train should travel. The automatic route selection is based upon predetermined constraints as well as traffic conditions.
By progressively removing more and more responsibility from the human operator, the systems disclosed in the referenced patents allow the operator to control more comprehensive territory than would have been possible under completely manual conditions. The term comprehensive is employed here to designate either larger and larger geographic areas or areas of greater complexity, or both. As those skilled in the art will realize, increasing the complexity of a railroad area, by for example adding further tracks and switches, or increasing the geographic extent of control, increases the rate at which decisions must be made at the controlling location as well as increasing the factors that must be taken into account in making those decisions.
However, as the number of train movements which must be controlled increases, the feasibility of employing manual control may be seriously questioned, even the minimum manual control required by the systems disclosed in the referenced patents. Furthermore, the system of U.S. Pat. No. 3,976,272 is suitable in situations in which an alternative route is available which is conflict-free or which will soon become conflict-free. The term conflict here refers to any situation in which one route would prevent the setting of another route, for example, where the two routes include a common track section or track switch. While the system of the U.S. Pat. No. 3,976,272 can cope with certain conflicts it is not designed to analyze the various options for effective conflict resolution. It should be apparent that, given a conflict, there is, of course, only one solution; one of the two trains must be delayed to enable the other to move past the conflicting point. Deciding which train to delay is not always simple, as many factors must be taken into account. For example, it is not at all unusual for these factors to include not only factors relating to the particular trains involved in the conflict, but also other trains which would be affected by delaying one or the other of the trains involved in the conflict.